Just to be clear on that matter and so I can, if need be, fix the wiki page - I remeber reading somewhere here on forums that cloak enchantment does not actually increase the resistance offered. Anyone knowns whether that's true?

Not true.
I just did some brief tests to make sure, and cloaks do indeed provide more resistance the higher they are enchanted much like how stat boosting armor pieces grant more points the more enchanted they are.

As an example with nothing but a leather cloak of fire resistance on you can step on a landmine and take thereabouts of 30 total HP damage from it. A cloak of fire resistance +5 will reduce this to about 10 damage.

System would indicate in graphic if person is mounted on horse or not.
Same system also show if person mounted on boar, elephant, polar bear etc.
Or if person mounted on ass.
Ivan find mounting on ass funny.

That reduction could have been from the additional AV. I seem to recall something along those lines myself. Should try asking Pent, he's done a fair bit of code-diving.

From what I recall that was the case.

Here's an old post I made after testing out different fire resistance values. I never did find out how exactly stacking multiple items for resistance works, but enchanting the cloak definitely does not provide better resistance, just higher AR.

Hmm. That is a point I didn't consider at the time.
Stacking resistance items definitely has a solid effect on resistances though, that I know for sure. As for how it works I do not know.

System would indicate in graphic if person is mounted on horse or not.
Same system also show if person mounted on boar, elephant, polar bear etc.
Or if person mounted on ass.
Ivan find mounting on ass funny.

So long as fire/electricity/poison/acid damage is variable, so should resistance be variable (via enchanting). Maybe to a point, since this is IVAN and we don't want people making themselves 100% fireproof, say.
As for cloaks of invisibility I can't really think of a good way to implement "variable invisibility" - maybe reaching certain thresholds should start blocking infravision, ESP etc.

System would indicate in graphic if person is mounted on horse or not.
Same system also show if person mounted on boar, elephant, polar bear etc.
Or if person mounted on ass.
Ivan find mounting on ass funny.

But since you already get additional protection from the AV, wouldn't that be redundant?

Only against that element though.

I'm not sure how useful a cloak + ring of elec/fire is against endgame mages and vet. dwarves, but from what I recall the resistance is already pretty high. so scaling elemental resistance might make you a little too fireproof.

There's also the Amulet of Elemental Protection, which is very powerful as well.